Apparatus and method for the automatic navigation of a sailing vessel

ABSTRACT

A navigation system for a sailing vessel which automatically sails the vessel from its present location to a destination location. The system responds to the prevailing wind conditions and characteristics of the craft to either sail directly or tack to the desired destination. Upon arrival at the destination location the system navigates the vessel to cause the vessel to keep a station in the immediate vicinity of the destination location.

United States Patent 1191 Bond 451 Nov. 13, 1973 APPARATUS AND METHODFOR THE 1 3,132,620 /1964 Court 114/39 AUTOMATIC NAVIGATION OF A SAILING3,173,395 3/1965 Lanrent. 114/39 VESSEL 3,295,487 1/1967 Smith 114/39 X3,505,577 4/1970 Hirokawa 114/144 R X [75] Inventor: Donald SpencerBond, Princeton, 3,517,285 6/1970 Kundler 318/588 N J 3,532,267 10/1970Tobin 235/1502 X [73] Assignee: RCA Corporation, New York, NY.

Primary ExaminerMilton Buchler [22} Filed 1971 Assistant Examiner-BarryL. Kelmachter [21] Appl. No.: 193,755 Attorney-Edward J. Norton RelatedU.S. Application Data [62] Division of Ser. No. 886,300, Dec. 18, 1969,Pat. No.

3,691,978. 7 [57] ABSTRACT A navigation system for a sailing vesselwhich auto- [52] Cl 114/39 1 14/144 235/5027 matically sails the vesselfrom its present location to a p 51 I 1 318/588 destination location.The system responds to the prei vailing wind conditions andcharacteristics of the craft 1 e o are 114/39 144 to either saildirectly or tack to the desired destina- 318/580 235/1502 15027 tion.Upon arrival at the destination location the sys- 343/102 112 112 PT temnavigates the vessel to cause the vessel to keep a l References Cited2:22): in the immediate vicinity of the destmatlon 10- UNITED STATESPATENTS 3,016,533 1/1962 Frank 343/112 R X 1 Claim, 4 Drawing Figures 60OTHER TELEMETRY WIND SATELL'TE SENSORS TRANSMITTER COMPASS 58 L 4O 44 li noPiiiR 25 A i 49 COUNT 1, 17 SAIL [5 I UNIT COMPUTER 4[ SERVO B I9 262 42 T j I RANGE AND ii RECEIVER EPHEMER'S OMPARATORFL, BEARING SAILINGDECODER COMPUTER COMPUTOR '2 l6 5 IDNOSPH ERE Pym 32 A T 37 470i 484 t)3 i 56 DEAD STORED l. CORRECTION EMORY RECKONlNG- SAILING f %Q COMPUTER2 COMPUTER 46 PROGRAM I 3 i I 1 "1 .11"" i s m i COMMUNICATION 'DIGITALCOMPUTER 22 PROCESSOR LINK SENSOR 11111111) TRANSMITTER PAIENIED IIIIVI3 I973 DIRECTION 3771.483 SHEET 2 OF 3 Fig. 2.

WIND DIRECTION F i 3 DIRECTION APPARATUS AND. METHOD FOR THE AUTOMATICNAVIGATION OF A SAILING VESSEL This is a division of application Ser.No. 886,300, filed Dec. 18, 1969, now U.S. Pat. No. 3,691,978.

This invention relates to the automatic navigation of a sailing vessel.

Automatic navigation systems" are known in the prior art. Such systemsgenerally fall into two classes, i.e., the remote control type and theautopilot type. In both types the operating procedure is to set orcompute a range and bearing from the present location to a destinationlocation and automatically move the craft directly between the twopoints. Some of .these prior art systems also provide compensation forthe change in heading or attitude of the craft in response to externallyapplied forces. Such forces may be the wind, ocean currents or even thechange in weight of a rocket as fuel is consumed.

Automatic navigation of sailing vessels is a complicated problem becausethe system must not merely compensate for prevailing wind and currentconditions, but in addition it must use the wind, either completely orpartially, as the motive force for the vessel.

When it is desired to tack a sailing vessel, that is to cause thevessel's head to swing through the wind, the rudder andasail must beadjusted to point the craft across the wind. As the vessel heels beforethe wind while tacking, a proper balance must be maintained or the craftwill capsize. Furthermore, the craft must have a certain velocity in thewater as it completes the tack across the wind or it will not be able tomake a followup tack which will result in an in irons or stalledcondition before the wind. Another complication in the tacking maneuveris that the vessel will capsize if the rudder is moved too quickly whenturning into the wind. I

In general, when sailing from one point to another, the rudder must befirstlpositioned to head the craft on the desired bearing. Once thedesired bearing is attained, the rudder is aligned with the fore aftaxis of the craft and the sail is positionedto catch the wind in amanner which will provide the greatest force vector in the direction ofthe desired bearing. Here, again, in bringing the craft about to thedesired bearing care must be taken never to head directly into the windor the craft will be stalled.

In both tacking and running free with the wind coming from the aftdirection, thesail must be periodically trimmed and in some instanceseven furled and unfurled.

As a result of the characteristics and problems inherent in sailing, theprior art does not disclose any practical automatic navigation systemfor a sailing vessel.

A very useful application for an automaticnavigation system for asailing vessel is in the field otsea buoys. Moored, unattended buoyshave long been used at sea as navigation guides to mariners. Some buoyshave included sensors for measuring air and water characteristics.Practically all such buoys have been restricted to relatively shallowcoastal waters where the problems of anchoring the buoys are not severeand where the buoysare readily accessible for maintenance.

More recently, experimental buoys have been built for mooring in thedeep ocean. Such deep-sea anchoring means are extremely expensive inboth initial installation cost and maintenance. The buoys themselvesmust be very rugged to withstand strong 'wind and waves and the inducedmooring stresses. If the buoy is located at a great distance from ashore base, the cost of sending a sea-going buoy tender is excessive.

With one embodiment of the present invention a system of buoys may besetout on the ocean from a shore base and ultimately sailed to desiredlocations wherein they may be left unattended for the telemetering ofmeteorological and hydrological observations.

The automatic navigation'system herein disclosed automatically sails avessel having a hull, a sail and a rudder to a given destination. Thestructure of the vessel determines a close haul angle of plus or minus Mwith respect to the wind directiontthe-plus and minus values may differif the vessel is asymmetrical about its fore-aft axis). Means areprovided for determining the present location of the vessel and therange and bearing from the present location to the destination. Thedirection of the wind is determined and the bearing angle B from thepresent location to the destination with respect to the wind isdetermined. Means are provided for positioning the sail and .the rudderof the vessel to sail directly to the destination when the absolutevalue of angle B is greater than the absolute value of angle M.Furthermore, means are provided for positioning the sail and the rudderof the vessel to sail to the destination on two or more tacks when theabsolute value of angle B is less than the absolute value of angle M.

In the drawings:

FIG. 1 is a block diagram of an automatic navigation system according toone embodiment of the invention;

FIG. 2 is a chart illustrating the conditions under which a vessel maybe sailed from its present location directly toits destination location;

FIG. 3 is a chartillustrating the conditions under which the-vessel musttack in order to sail from its pres-' ent location to its destinationlocation; and

FIG. 4 is a chart showing the manner in which the vessel station-keepsat the destination location.

The invention herein described may be practiced with a vessel having asail and a rudder, and is especially useful with a craft having a rigidor semi-rigid sail. Such a craft is disclosed in United States patentapplication Ser. No. 794,589, now U.S. Pat. No. 3,556,035 assigned tothe same assignee as the present application. The craft in thereferenced patent application is further characterized by asubstantially circular hull structure which, in combination with thesail and rudder configuration allows the vessel to be oriented towards adesired location by setting the sail and rudder in predeterminedpositions. Utilization of the referenced craft permits a simplificationof the structure for practicing the present invention in the preferredembodiment shown herein.

The substantially circular hull shown in the referencedapplication isnot essential for practicing the present invention. A conventional yachthull may be used with the present invention but, for reasons set forthherein, a conventional yacht hull is less desirable.

Similarly, any wind energized propulsion means, such as an airfoil, acloth sail, or Flettner rotor may be substituted for the sail in thereferenced application. However, when a sail system of more complicatedhandling characteristics is used, several additional servomechanismcontrols will be required. The additional controls will requireadditional stored programs for operation thereof.

There are many known methods for accurately determining the presentlocation of a craft in the water. One of the modern approaches toposition determination, and the one preferably used in the navigationsystem herein disclosed, is the utilization of earth orbitingsatellites. An appropriate satellite system for this application is theNavy Navigation Satellite System, also known as TRANSIT, which isdescribed by T. A. Stansell, Jr. in the Proceedings of the NationalMarine Navigation Meeting, Oclf. 11-12, 1967, at pages 36-60, publishedby the Institute of Navigation in Washington, DC, U.S.A.

Other radio navigation systems, such as hyperbolic systems like OMEGA orLORAN may be substitued for the Transit system. Alternatively, pointlocation stations, such as sonar transmitters disposed at predeterminedpoints on the ocean bottom, maybe employed for providing the desiredlocation information.

If four satellites are in appropriate polar orbits, one of them comesinto the view of any location on the surface of the earth every one ortwo hours. During one satellite pass, it is possible to obtain anavigation fix at a terrestial location with a very small error.

In FIG. 1, a satellite passes within the radio line of sight of thepresent location of the sailing vessel and transmits appropriatenavigation and timing information. Antenna 11 located on the craftreceives the transmitted signals and provides the information toreceiver 12 via line 13. Receiver 12 provides the incoming signals todata processer 14 via lines 15, 16 and 17.

Line is connected to the input terminal of Doppler count unit 18.Doppler count unit 18 determines the total number of cycles of theheterodyned Doppler signal during a selected time interval.

Line 16 is connected to the input terminal of an ephemeris decoder 19which translates the digital code representing the up-to-date geometricelements of the satellite orbit into computer language.

Line 17 is connected to the input terminal of an ionosphere correctioncomputer 20. Ionosphere correction computer 20 provides a correction tothe Doppler count via line 21. The correction for ionospheric conditionsis based upon the comparision of signals at two received frequencies.Output signals from the data processor 14 are provided at the inputterminals to a general purpose digital computer 22 via lines 23 and 24.

Lines 23 and 24 carry navigation 'fix information to a section of thegeneral purpose digital computer 22 termed the latitude-longitude().,p.) computer 25. Latitude-longitude computer 25 determines thepresent position of the vessel and encodes the resulting coordinates andprovides corresponding signals on lines 26 and 27.

The latitude and longitude coordinates of the desired location ()t .1.are stored in the computer memory 28. Access to the computer memory 28may be had locally or via a remote command transmitter 29 linked to thememory by way of the communications link 30. Link 30 may comprise aradio receiver cooperating with transmitter 29. The stored coordinatesof the denates of the present location and the coordinates of thedesired location on line 33.

The signals on line 33 are provided to a range and bearing computer 34.Range and bearing computer 34 performs a trigonometric transformation togive the range and bearing from the present position to the desiredposition. In suitable linear units, the range R is given by The bearing(relative to true north) is given by A, where A tan Ak/Ap.

The reference direction for the range and bearing computer 34 isprovidedby the magnetic compass 35. The corresponding signal is providedto the range and bearing computer 34 from the compass 35 via line 36.

When the navigation data source is intermittent, as is the case where anorbiting satellite is the data source, means must be provided togenerate the range and bearing continuously between the times of fixes.This function is performed by dead reckoning computer 37, whichcontinuously computes the range and bearing to the destination.

The dead reckoning computer 37 obtains information as to the speed ofthe craft through the water by the commonly used technique of a taffraillog water current sensor 38. Sensor 38 comprises a propellor andelectrical generator whose speed varies linearly with v, the speed ofthe craft through the water and which measures by counting totalrevolutions, the distance d traveled through the water during a timeinterval I The corresponding signal from sensor 38 is coupled to thedead reckoning computer 37 via line 39. Water current sensor 38 alsoincludes a vane for sensing the direction of movement of the water withrespect to the fore-aft axis of the craft.

sired location are represented by a signal coupled from I Computer 37together with sensor 38 performs the integration (I I 2 wit and alsoresolves d into north and east components of distance travelled withrespect to the water:

d, 01 cos A I 11,, d sin A where A is the bearing of the fore-aft axisof the vessel with respect to north. The computer 37 obtains a northreference signal from compass 35 via line 40 with suitable correctionfor magnetic variation. Using components d, and d determined at any timethe approximate position of the craft between navigation fixes iscomputed.

The continuously generated signals corresponding to the range andbearing to the destination are coupled to the sailing computer 41 vialine 42. In addition, a signal corresponding to the wind direction,generated in the wind direction sensor 43, is provided at an inputterminal of the sailingcomputer 41 via line 44. Wind direction sensor 43is provided with a reference direction signal from compass 35 via line45.

Depending upon the prevailing wind conditions and the bearing to the newlocation, appropriate sailing maneuvers for the most efficient sailingof the vessel are called up from the stored sailing program 46. Thestored sailing program is entered via line 47 and the appropriatesignals corresponding to the desired maneuvers are coupled to thesailing computer 41 via line 48.

The stored sailing program 46 is a look-up table wherein the appropriatepositions of the sail and the rudder with respect to an arbitrarilydetermined foreaft axis of the craft are contained. The look-up table isempirically determined for the particular craft.

The appropriate positions of the sail and rudder for the most efficientsailing of the craft are initially experimentally determined and enteredin the look-up table.

Specifically, the preferred craft previously mentioned has, by virtue ofits construction, the ability to traverse the distance between thepresent location of the craft and another location by a single settingof the sail and a single setting of the rudder in predetermined positonswith respect to the arbitrary fore-aft axis through the substantiallycircular hull. This particular craft can head into the wind withoutbeing stalled even though no headway can be made in a sector defined bythe close-haul angle of the craft and centered about the direction ofthe wind. The sail on the preferred circular hull craft can be turnedclockwise or counter-clockwise with respect to the wind directionwithout detrimental effects. Furthermore, the sequence of setting thesail and the rudder and the rate of movement of both has been found tobe immaterial for this particular craft.

Therefore, for each angle, B, the sailing program 46 provides signals tothe sailing computer 41 corresponding to an experimentally determinedsa-il position and rudder position.

Sailing computer 41 provides corresponding signals to the sail servosystem 49 via line 50. Sail servo 49 controls the orientation of thesail'52 via the mechanical link 51. Simultaneously, the sailing computer41 provides corresponding signals to the rudder servo system 53 via line54. Rudder servo 53 orients the rudder servo system 53 via line 54.Rudder servo 53 orients the rudder 55 via the mechanical link 56.

All of the functions described by the blocks contained within thedigital computer 22 are internally performed in computer 22. There aremany general purpose digital computers readily available for performingthe functions of digital computer 22. One such com-- puter is the PDP-8computer built by the. Digital Equipment Corporation, of Maynard,Massachusetts. The programming of such a digital computer to perform thesteps previously described is well known in the programming art.

Sailing craft are characterized, as a result of their individualstructure, by what is termed as a close-haul angle. The close haul angleof a sailing vessel is defined as the closest angle to the directionfrom which the wind blows which will allow the vessel to gain distancetoward the windward direction. A sailing vessel is unable to saildirectly intothe wind, and the close-haul angle of plus or minus M withrespect to the direction from which the wind blows (the plus and minusvalues may differ if the vessel is asymmetrical about its foreaft axis)defines a sector within which the vessel may not sail directly to anypoint contained within the sector.

When a sailing craft does in fact head into the sector defined by theangles plus and minus M at low speed the craft will come to a stop,heading into the wind, and is said to be stalled or in irons." When acraft is in irons it cannot turn port or starboard but will drift slowlydownwind. The vessel will be able to get out of irons only withdifficulty and with the application of some external force or change inthe prevailing wind conditions.

When it is desired to sail. a craft to a location within the sectordefined by the close-haul angle the craft must tack in order to reachthat location. One or more tacks may be necessary depending upon therange and prevailing wind conditions.

Referring now to FIG. 2, together with FIG. 1, the vessel is launchedfrom a land base at point L. At some time thereafter, satellite 10appears above the horizon at the location of the vessel and the onboardequipment computes the present'coordinates ().,p,) of the point P. Thedestination coordinates ()t .4. of the point D are stored in the memory28. The wind direction is at the angle C with respect to north. Sailingcomputer 41 determines that the bearing B (with respect to the winddirection) to the destination is greater than the closehaul angle M.Stored sailing program 46 calls up the appropriate sailing maneuvers,that is, the sail position and the rudder position to sail directly frompoint P to point D at a bearing of A with respect to north and a rangeR. With the sail 52 and the rudder 55 positioned in accordance with thecommands from the sailing computer 41, the vessel starts to sail acourse directly to point D.

As the vessel sails the dead reckoning computer 37 continuously computesthe approximate location of the vessel by resolving the componentsd, andd shown in FIG. 2.

Returning to FIG. 1, a telemetry transmitter 57 is provided to transmitthe continuously generated signals corresponding to range and hearingfrom computer 34 on line'58.

A suitable antenna 59 is coupled to the telemetry transmitter 57 forthis purpose. The signals on line 27 corresponding to the accuratelydetermined present position are also provided at transmitter 57 in orderto relay this information to a remote monitoring station. In addition,signals corresponding to the parameters determined by other sensors suchas sensors 43 and 38 are provided at transmitter 57 viav line 60 forrelay to the monitoring station.

Referring now to FIG. 3, together with FIG. 1, satellite 10 passeswithin the radio line of sight of the vessel and the present coordinates(Lu) of the point P are determined. The coordinates 0. 1. of thedestination D under these particular conditions lie within the sectordetermined by the close-haul angle of plus and minus M. The vesseltherefore cannot traverse the range R on a bearing of A with respect tonorth under these prevailing wind conditions. Therefore, the storedsailing program 46 will provide the necessary sail and rudder positioninformation to enable the vessel to tack to the destination location D.

The sailing computer 41 determines the existence of the conditionsrequiring tacking by comparing the original bearing A with respect tonorth, provided by the range and bearing computer 41, with the presentwind direction provided by sensor 43. When tacking is required, sailingcomputer 41 computes an offset to the original bearing A to determine anew bearing A Sailing computer 41 also computes a new range R which isarbitrarily programmed to be approximately 0.7 of the original range Rin the case where it has been decided to sail to the destination D intwo tacks.

The new bearing A is translated into bearing B, with respect to the windin computer 41. Bearing B and range R are provided to the stored sailingprogram 46 via line 47 and the sail 52 and rudder 55 are positionedaccording to the look-up table.

The vessel will sail on the first tack until the distance R has beentraversed or until the satellite 10 passes over, whichever comes first.

If the satellite 10 passes over before the first tack is completed a newrange and bearing will be set forpoint D based on the updatedinformation.

If the distance R is traversed before the satellite 10 passes over thesystem will compute the new bearing B and range R when the vesselarrives at point P. The vessel arrives at point P when the continuouslygenerated range information from the dead reckoning computer 37 matchesthe computed range R,.in the sailing computer 41.

At point P.', the system determined the range R and bearing 8, withrespect to the wind and if the bearing B, is now beyond the close haulsector the craft will sail directly to the destination point D. If thecraft is within the close haul sector at point P' the system will againinitiate the procedures to sail from point P to point D on two tacks.Changing wind conditions may cause the bearing B at point D to fallwithin the close haul sector.

Once having arrived at the destination point D, it is desired tomaintain or station-keep the vessel in the immediate vicinity of point Din order to perform its meteorological and hydrological functions.

Referring to FIG. 4, a preferred method of stationkeeping is shown.Assume the craft is at station at time i=0, the time of the initialnavigation fix. In an x, y coordinate system the selected station is atx=0, y=0. The wind vector is along the yards and is directed toward thenegative direction. Navigation fixes are made at equal time intervalsA2,, starting at t=0.

Starting at station 0, having x, y coordinates 0,0 the vessel is sailedat 90 with respect to the wind vector for a time At/2. Course reversalsat times of T=At, 2At,

are made until the next satellite passes over and a navigation fix isobtained at t=t,.

If ocean currents are not appreciable the craft will sail back and forthbetween the points A and B in FIG. 4.

At the time of the navigation fix, t=t,, a retrace course back to thestation at 0, 0 is determined by the system. FIG. 4 illustrates theretrace courses when currents or other perturbing forces cause thevessel to drift. If the bearing from the craft location, at time t,, tothe point 0,0 lies outside of the close-haul angle sector, then thecraft will return on a direct path to its desired station. However, ifthe bearing of the return course lies within the close-haul sector thenthe craft will tack to its desired station as shown in FIG. 4. Point Pin FIG. 4 is determined by the continuously generated information fromthe dead reckoning computer 37. In this manner, the sailing craft willbe kept within a few tenths of a nautical mile from the desired stationdespite any drift caused by water currents.

Point C in FIG. 4 is also determined approximately by the dead reckoningcomputer 37. However the position so determined will differ from themore precise fix from the radio navigation system. The difference inposition or closing error provides a measure of the magnitude anddirection of the prevailing ocean surface current. The system of thepresent invention thus serves as a sensor of ocean current.

With the wind and ocean currents in a more favorable orientation withrespect to the vessel, the craft will sail between points A and B inFIG. 4 and remain extremely close to the desired station at 0,0.

What is claimed is:

l. A method of automatically navigating a sailing vessel without therequirement of human intervention to a given destination, said vesselhaving a hull, a sail and a rudder, the structure of said vesseldetermining a close haul angle of plus or minus M with respect to thewind direction, which comprises:

automatically determining the present location of said vessel fromelectrical navigation signals provided from a source remotely locatedwith respect to said sailing vessel; automatically determining the rangeand bearing from said present location to said destination;

automatically determining the wind direction and the angle, B, of thebearing from said present location to said destination with respect tosaid wind direction;

automatically positioning said sail and said rudder, in

accordance with the predetermined positions for said sail and saidrudder stored in a memory means, to sail said vessel directly to saiddestination from said present location when the absolute value of saidangle B is greater than the absolute value of said angle M; and

automatically positioning said sail and said rudder, in

accordance with other predetermined positions for said sail and saidrudder stored in said memory means, to sail said vessel on two or moretacks to said destination from said present location when the absolutevalue of said angle B is less than the absolute value of said angle M.

1. A method of automatically navigating a sailing vessel without therequirement of human intervention to a given destination, said vesselhaving a hull, a sail and a rudder, the structure of said vesseldetermining a close haul angle of plus or minus M with respect to thewind direction, which comprises: automatically determining the presentlocation of said vessel from electrical navigation signals provided froma source remotely located with respect to said sailing vessel;automatically determining the range and bearing from said presentlocation to said destination; automatically determining the winddirection and the angle, B, of the bearing from said present location tosaid destination with respect to said wind direction; automaticallypositioning said sail and said rudder, in accordance with thepredetermined positions for said sail and said rudder stored in a memorymeans, to sail said vessel directly to said destination from saidpresent location when the absolute value of said angle B is greater thanthe absolute value of said angle M; and automatically positioning saidsail and said rudder, in accordance with other predetermined positionsfor said sail and said rudder stored in said memory means, to sail saidvessel on two or more tacks to said destination from said presentlocation when the absolute value of said angle B is less than theabsolute value of said angle M.